While diabetes self-management has been improved and refined over the last 30 years, many persons with T2DM continue to have difficulty in achieving glycemic goals. Obstructive sleep apnea (OSA) has a high prevalence among adults with type 2 diabetes (T2DM) and is associated with excessive daytime sleepiness, impaired mood, decreased vigilance, and reduced functional outcomes. The degree that OSA affects diabetes self-management, a known determinant of glycemic control, remains unstudied. The most effective treatment for OSA, continuous positive airway pressure (CPAP), results in improved self-reported daytime functioning. However, the effect of CPAP treatment on reception of diabetes education remains unknown. The underlying premise of the proposed study from this new investigator is that OSA hinders diabetes self-management in adults with T2DM. This study expands on our pilot/feasibility study that suggested that CPAP treatment is associated with decreased fatigue, increased physical activity, and improved glucose control. Our goal is to improve understanding of the effect of OSA on diabetes self-management and to determine the efficacy of CPAP treatment in improving diabetes outcomes in adults treated with CPAP compared to those on sham- CPAP. We propose to enroll 210 adults (50 percent female; 40 percent minority) with T2DM and moderate-to-severe OSA (apnea + hypopnea index > 15) who have suboptimal glycemic control (A1C e 7.0 percent) for a double blind, randomized, placebo-controlled trial to determine if diabetes self-management outcomes and glycemic control are better in subjects with OSA who are treated with CPAP and receive diabetes education and counseling compared to control subjects who are on sham-CPAP and receive diabetes education. We will compare the effectiveness of the intervention after 6 weeks and 12 weeks on measures of glycemic control, retention of information taught during the diabetes education sessions, lifestyle behaviors required for optimal diabetes control, reported monitoring of self-management activities, physical activity, and diabetes-related distress. We will explore whether the average nighttime use (adherence) of CPAP, sleep quality, daytime sleepiness, mood, and vigilance mediate the effect of CPAP treatment on glycemic control and diabetes self-management outcomes. We will also explore if adherence to CPAP is associated with outcome measures of glycemic control and lifestyle behaviors in the entire sample after 24 weeks of therapeutic CPAP. This study uses objective measures to measure CPAP adherence, physical activity, vigilance, and glycemic control. After 12-weeks, subjects who were originally on sham-CPAP will be crossed over to active treatment. The overall impact of this study will be increased knowledge about the effect of sleep apnea on diabetes self-management. Expanding our understanding of the effect of sleep disturbances on diabetes self-management may lead to improved guidelines for screening and treatment of OSA in the increasingly large portion of the population with diabetes.